Recent content by Quant

I have a collimated beam from a laser diode d= 10 mm and want to narrow it down to 1 mm. I suppose to use a lense to focus it and then use a lense to collimate it with d=1mm but this lense must have focus distance of 1 mm?? Are there such lenses? Or I must do it in other way?

Thank you. I see. Collimating is ok but how to bring the beam size to 2 mm. Of course I will use a lense to focus the beam to a point but then I must use a lense with very short focus distance (maybe 1 mm) to get a parallel beam after it which will have a diameter of 2 mm. Are there such lenses?

I would be very thankful if somebody helps me with some practical advices about producing twin photons? I know that twins are produced after a laser ray is directed on a BBO crystal. After the BBO there are two rings of photons and the twins are in the intersection of the rings. 1. I wonder in...

Why should we put a single slit before DS? If the (say idler) photons of entangled pairs do not make DS interference pattern one will disentangle the signal photons and the idler must start to do DS interference. One could send FTL easy then. Consider 10 groups of 1000 idler photons. One can...

There is not such thing as Feynman rules. What I use is just a working slang. I could say the 'rules for constructing the path integrals' but it's too long don't you think? There are the Feynman path integral (which I know exactly how to calculate in one particle case) and there are 2 rules...

Thanks Dr. Chinese. Are you saying we can not destroy photon 1 of a entangled pair and leave photon 2 on an infinite journey in all inertial reference frames? Where it should be an unentangled 'normal' photon which will begin to interfere with itself?

And when the one photon (2) is registered in the detector (c) there would be just one photon (1). Does it has no amplitude? Can Feynman rules not say where we would chance to detect it?

The problem here is strictly in Feynman paths not any other formulations. So I want to know just the amplitude of photon 1 from 'a' (birth of twins) to 'b' (detector). Photon 2 starts also from 'a' but can go to either 'b' or 'c' tru point 'd' (BS 50/50). If it goes to c (is registered there)...

Maybe. But in experiment like DSE and MZI one measure the positions by positioned photon detectors. I am interested in only these experiments.

I understand this as one particle going two distant paths at the same time together.(e.g photon1 goes also the paths of photon2 which would be otherwise inaccessible for it?

Is the Feynman integral in configuration space or in momentum space?

I don't know Feynman reformulation of QM about entangled pair. For single particle it is 100 % sure that we consider all paths between any two point (usually emitter at a and detector at b) and as the path is surely function of xyz one is in (configuration) space. I don't see anywhere momenta...

Why is Demystifier talking about configuration space then?

So you think the amplitude of the other particle should be added? Suppose photon 1 of the twin pair goes to a beam splitter BS1 and photon 2 can go in the other port of the BS1 but it doesn't (it goes tru a BS2 which outputs are on BS1 and on a point c and is registered after a while in point...

So you think the amplitude ofar the other particle must be added?